Tuesday, January 06, 2009

Not long after Boof Bonser's sentence to the bullpen, I analyzed Boof's pitching through the use of pitch f/x. My conclusion at the time was that his slider, a pitch he threw nearly a quarter of the time to righties, was flattening out at that time in the season, resulting in an unexpectedly high .288/.322/.441 batting line against righties as of June 14th. Still, at the conclusion of the season, Bonser had improved his approach against the same-sided opponents, dropping his batting line against to .260/.295/.405, suggesting that he had regained his slider and his repertoire was playing well in the 'pen, a sign that he could be capable of assuming a meatier role in the 2009 bullpen.

In addition to this in-season improvement, there are several other statistical indications that -- as the Counting Crows song so eloquently puts it -- this year could be better than the last. For starters, his fielding independent metric of 4.51 was much better than his swollen 5.93 ERA. Secondly, his left-on-base percentage of 57.9% and those with severely low LOB% sometimes rebound the following season. Lastly, Bonser's candidacy as a solid bullpen contributor is buttressed by his minor league legacy. Over the course of seven minor league seasons, Bonser has struck out 916 batters in 884.1 innings while walking just 398. His last full season at AAA in 2005, Bonser led the International League in strikeouts.

It is hard to refute those three cited examples as justifiable reasons for Bonser being anything but an excellent internal candidate for the vacant set-up role. However, if you look closer at his numbers, there are two glaring problems with Bonser's game that supersedes his ability to be an effective reliever in high leverage situations: (1) He is useless against left-handed opponents and (2) He can't pitch from the stretch.

The first is his approach against left-handed opponents.

vs LHB

Bonser

RHP League-Average vs LHB

2006

.251/.305/.451

.279/.349/.446

2007

.349/.407/.563

.275/.349/.438

2008

.315/.378/.486

.269/.346/.430

Lefties are a demographic that had not given Bonser trouble in 2006 but were suddenly a blight on his landscape in 2007. In his first year, Bonser had limited lefties to a .251/.305/.451 batting line. In the subsequent season, it swelled to .349/.407/.563. Prior to his demotion to the bullpen, Bonser had improved upon his 2007 numbers with a .297/.322/.441 line. Unfortunately he regressed in the 'pen and at the 2008 season's end, lefties had hit a collective .315/.378/.486. If you are looking for a silver-lining, it was a tad better than his 2007 numbers on the whole, however, the bulk of the destruction happened when Bonser was in relief.

More recently, in 12 starts in 2008, Bonser had thrown 66.1 innings with a 42/20 K/BB and high 7.08 RA but a low .267/.316/.418 opponent batting line. Following his transition to the bullpen, Bonser threw 52 innings and compiled a 55/16 K/BB ratio but still posted a 6.02 RA as opponents batted .307/.353/.474 off of him. As I mentioned above, Bonser's opponent average against right-handers DROPPED when converted to a reliever. On the other hand, up until June 14th lefties were hitting .297/.322/.441. At the end of the season, it rose to to a firm .315/.378/.486. The inflated batting line as a reliever came in direct result of left-handed opponents.

The second problem is that he is atrocious when pitching from the stretch (something that relievers are requested to frequently, often with the game on the line). Similar to his left-handed struggles, pitching with runners on manifested itself after his rookie season.

Runner On Base

Bonser

League-Average

2006

.267/.319/.466

.274/.348/.425

2007

.294/.367/.478

.277/.350/.430

2008

.322/.349/.467

.274/.348/.425

What seems to be given him the biggest problem is when runners are on first - more so than any other base path alignment.

Runner On First

Bonser

League-Average

2006

.295/.313/.526

.277/.335/.435

2007

.360/.416/.640

.284/.342/.442

2008

.369/.411/.500

.277/.348/.425

In addition to the higher batting line, Bonser's stolen base rate skyrocketed too from 57% SB% in 2006 (4 in 7), 61% in 2007 (11 in 18) and 100% in 2008 (11 of 11). Considering that limiting a baserunner from scoring may be more important in the later innings in a high leverage situation, Bonser appears to be a liability under these circumstances. Clearly this is a bigger problem than his weight. This is a mental issue.

That said, the benefit about being a reliever is that you do have a manager that can use you at appropriate times as to not exacerbate your weaknesses. Bonser can be inserted during times when three right-handed batters are due up. Naturally, this leaves him susceptible to the occasional left-handed pinch hitter, but those are seldomly fearsome. Where Bonser becomes an issue is when he allows one of those hypothetical batters to reach base and forces Gardenhire to select from allowing Bonser to continue to face Hafner, Martinez, Thome, etc. with a runner on first -- which, as we've seen above, is a recipe for disaster -- or bring in a left-handed situational reliever (Breslow/Mijares), if any are available. That begs the question, how common is it that three right-handed batters are batting in succession without a leftie giving them reprieve? How likely is it that Gardenhire will save Breslow or Mijares until after Bonser pitches? In the end, a solid 8th Inning Guy, like a closer, should not need this much management. Bonser is simply not that guy.

About OtB

"Parker Hageman is the Michael Cuddyer of Twins bloggers -- not the flashiest guy out there, but a solid everyday player. Hageman produces spot-on analysis ... relying on in-depth stats and lots of charts. He takes a sober, performance-based view of players, letting others fall for a player's heart or his leadership skills in the clubhouse. Hageman is one of the four pillars holding up the Star Tribune's TwinsCentric blog."